1. Field of the Invention
This invention relates to electrical protection devices and more particularly to a device operable with the ballast of a high intensity, gaseous discharge lamp or lamps, wherein such device does not insert an electrical characteristic to the circuit and does not have to be reset or replaced once the protection against a large electrical charge has occurred.
2. Description of the Prior Art
A high intensity, gaseous discharge lamp operates in conjunction with a ballast circuit for starting and maintaining operation of the lamp. The characteristics of the lamp and the starting and operating circuit are such that it is not uncommon that a very rapid change of current and/or voltage occurs. When this happens, there is sometimes a tremendously high charge developed across the ballast, which usually includes some sort of a transformer arrangement. For exemplary purposes only, it can be visualized that this large charge develops across the secondary of a transformer.
In addition to the normal high voltages or charges that exist in an HID lamp circuit, which may very normally include quite high starting pulses, extraordinary surges may occur due to lamp failure or other component failure, high voltages caused by mistakes in connecting the circuit components and the like. Such surges can result in exceedingly high voltage and/or current change rate, or di/dt, problems in the circuit.
A large voltage across the secondary of the ballast transformer can damage or even destroy the ballast and/or other components in the circuit. When this happens, it is sometimes difficult to detect what has been damaged or destroyed. Further, the location is often difficult to get to, such as at the top of a long pole, in order to replace a burned out ballast. Fuses and circuit breakers, which have to be replaced or reset, although saving the circuit components, do not make it any easier to attend from a maintenance point of view. It is possible, although not done in practice, to use existing spark arrestors that are employed in other applications. However, such known arrestors would add capacitance to the circuit, thereby changing the characteristics of the circuit. In addition, known prior art arrestors carbonize in use, causing additional problems of inserting an electrical component, the value of which changes, thus creating the possibility of establishing a completed short that would cause substantial and permanent damage and require the replacement maintenance that is often difficult, as described above.
As a result of all of the above, most high intensity, gaseous discharge lamp installations today are not protected against the sudden changes of voltage or current described above, which changes not infrequently occur.
Therefore, it is a feature of the present invention to provide an improved electrical spark arrestor, particularly well-suited for protecting a high intensity, gaseous discharge lamp circuit.
It is another feature of the present invention to provide an improved electrical spark arrestor that inserts no electrical characteristics into the protected circuit and which does not need resetting or replacement, even after a number of discharges, and which further does not appreciably carbonize.